


Abyss

by Askellie



Series: Leviathan AU [3]
Category: Undertale (Video Game)
Genre: Alternate Universe - Merpeople, Bad Sanses | Nightmare's Gang (Undertale), Crosstale Sans (Undertale), Dreamtale Nightmare Sans (Undertale), Dreamtale Sans | Dream (Undertale), Dusttale Sans (Undertale), Horrortale Sans (Undertale), Killer Sans (Undertale) - Freeform, Kracken Nightmare, Leviathan AU, M/M
Language: English
Status: Completed
Published: 2021-02-28
Updated: 2021-02-28
Packaged: 2021-03-19 09:07:11
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 3,413
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29748177
Author URL: https://archiveofourown.org/users/Askellie/pseuds/Askellie
Summary: There’s so muchnothingit’s almost an entity unto itself. The weight of water bearing down on him is making his chest feel tight, making him remember things he doesn’t want to.--Cross doesn't cope well in deep, dark water.
Relationships: Sans/Sans (Undertale)
Series: Leviathan AU [3]
Series URL: https://archiveofourown.org/series/2152734
Comments: 34
Kudos: 221





	Abyss

**Author's Note:**

> Leviathantale belongs to Skumhuu!

“Come on,” Killer says, gliding up alongside Cross so closely that for a moment their tails are flush together, pectoral fins entwined. “Leave the big knife at home. We’re taking you on a _real_ hunt today.”

There’s a ripple of hungry anticipation in the water that prickles along Cross’s scales. Reluctantly, he leaves his sword beside the algae bed at the base of the grotto, feeling strangely heavier without its solid, comforting weight on his back. 

They head out, the rest of the shiver falling easily into an arrowhead formation. Horror leads the way, his sharp senses already tuned to any signs of possible prey, while Dust and Killer fan out on either side of him, guarding the flanks. Cross is left to fall awkwardly in behind them, struggling against the backdraft of their powerful tails cutting through the water. He’s forced to swim slightly lower, the displaced current of their momentum pressing down on his shoulders and dorsal fin in a way that sparks a faint feeling of unease. 

They don’t follow the craggy rise that Cross normally uses for his hunts, where murky light still manages to reach from the surface high above. Instead they head deeper into Nightmare’s domain where Cross wouldn’t dare explore on his own. Dream has shown him some of the paths, his golden glow keeping the hungry shadows at bay, but without the little goldfish’s comforting presence the darkness makes the abyssal plain look endless and empty. Cross represses a shudder and swims a little faster, trying to stay close to the others.

Though it’s not easy to orient himself in unfamiliar territory, he can feel the change in depth by the way the cold is starting to sink into his bones. The water feels heavy and dense, filling him with a strange sense of claustrophobia even though there’s nothing but empty space around him.

(There’s so much _nothing_ it’s almost an entity unto itself. The weight of water bearing down on him is making his chest feel tight, making him remember things he doesn’t want to.)

Abruptly Horror dives, pivoting towards the seabed below. Killer and Dust turn seamlessly to match him, but Cross’s reaction is slower. He tells himself he’s just not used to the unspoken signals used to direct the shiver’s movements and not because dread is making his body slow and clumsy. Thankfully the others don’t notice, all their attention fixed on the narrow fissure Horror has guided them to, leading to an even deeper level of the trench

“In here,” Horror murmurs. “Can smell them.”

Cross inhales as deep as he can, which isn’t much with how compressed his ribs feel. There’s something in the fissure, though it doesn’t register immediately as prey to his untrained nose. It’s a faint, musky scent, like an old kelp forest that’s starting to rot. 

“Bet I catch one first,” Killer taunts, and dives into the fissure, heedless of the darkness.

Horror lets out a faint, aggravated growl and darts after him, needing to angle his larger body more carefully through the gap. 

“Idiots,” Dust murmurs to Cross with a fond roll of his eyelights. Unlike the others, he seems to remember Cross isn’t actually experienced with their hunting grounds. “Careful down here. Most threats are smaller than we are, but a few of them are poisonous. Won’t kill you, but hurts like a bitch. Stay away from the walls. They like to hide in the crevices.”

Cross nods tightly, not trusting his voice to give an unwavering reply. Uneven eyelights bore into him, pupils contracting like maybe Dust has caught a whiff of the apprehension (fear) Cross is struggling to push down, but after a moment he turns away, diverted by the distant cackle of Killer’s laughter.

“Come on,” Dust says, fingers briefly brushing against Cross’s own in a silent encouragement that’s kinder than his gruff tone. “Don’t fall behind.”

Dust dives into the crevice and Cross follows hastily in his wake, close enough that the pale tip of Dust’s tail nearly smacks him in the face. He grudgingly allows a little more distance, trying to focus on the rippling displacement of current from Dust’s movement instead of squinting through the increasingly murky water.

Cross knows he’s too reliant on his sight. It’s a weakness born from his captivity, spending too much time with his head above water and in too-small tanks. Even in his early days of freedom, he’d stuck to shallow water and hunting in the daylight hours. It’s almost shameful how little he knows about his own predatory senses. He shouldn’t _need_ to see; he knows the others simply extinguish their pupils when hunting, eliminating the little pricks of light that would give away their position and relying purely on smell and motion to track their prey in the darkness of Nightmare’s domain.

Dust seems to have no trouble navigating. If Cross closes his eyes, he can feel his shivermate; the graceful undulation of his body, the efficient way he’s slicing through the water, the fainter ripples of the pilot fish that always clings to his side. Stretching out his awareness further, Cross can feel a distant flurry of movement, more dispersed and chaotic than Dust’s purposeful stride. He wonders if that’s the prey they’re tracking, or perhaps it’s the thrashing of Killer and Horror already partaking in the hunt. There’s no hint yet of blood spilling in the water, but Cross’s jaw clenches with anticipation. 

The distant motion teases him, sending an excited quiver down his spine. For a moment he imagines diving into the fray, flanked by his shivermates, sinking his teeth into something warm and soft, exalting in the thrill of the chase and the glorious taste of fresh prey. Hands and fins stroking him with approval as they share the kill in messy, bloody bites, the rumble of their hunting song echoing in the crevice as both celebration and warning of their success-

The sudden swell of a cold current washes over him like a slap of reality, and Cross’s red-tinted fantasy evaporates into a void of black as he accidentally opens his eyes.

It’s so _dark_.

The stroke of his tail falters, leaving him stalled in the water, and he immediately loses sight of Dust ahead of him. He knows the walls of the crevice are banking him on either side, but mindful of Dust’s warning he kept his distance from them. The heavy shadows give an illusion of being suspended in nothingness whilst simultaneously feeling trapped.

( _stuck in a sinking cage, bruised, disoriented, helpless_ )

The heavy pressure of deep water is suddenly suffocating, thick and cloying as he tries to filter it through his gills, but his lack of momentum in the water means he’s already straining for breath. He’s all out of rhythm, his limbs starting to jerk as each shallow gasp leaves him feeling dangerously dizzy and even closer to the brink of panic. Faintly, he realises his fear-frozen body is starting to sink, taking him deeper into the abyss.

( _he’s alone and lost -- abandoned or simply forgotten, he doesn’t know, but endless, agonising minutes drag into hours, then into days..._ )

Unthinkingly, he’s curled in on himself, his tail folded up to his torso and skull hidden beneath his arms as if he can shield himself from the nothingness. He can’t even tell if his eyes are open or closed anymore; all he can see is around him is a blackness so encompassing it feels like it’s smothered the rest of his senses. His nose is full of the sharp-sour scent of his own fear, and his skull is hammering with the wild pulse of his soulbeat. The subtle ripples of movement in the water now feel jarring, almost painful against his scales, like the water is roiling with electricity, his nerves blown out and reeling from the intensity. A sound catches in his throat, strangled to silence by the lack of air and the choking knot in his throat like the vicious clasp of the collar he used to wear.

( _slowly starving, suffocating, his desperation fraying into despair and then a madness of resentment and loneliness and grief, knowing he’s going to die and that his life meant nothing._

_hating Gaster with every inch of his being but silently begging, bargaining, praying to be found, if only to know that his existence meant something to at least one person even if it was someone he despised._

_but nobody came_ )

Except a sudden jolt to his dwindling awareness tells him that somebody did come. There’s a fierce grip on his ribs and waist, crushing his stiff, unresponsive body against another that’s solid and warm against his own. Between the wheezing rasps of his breath, Cross catches fragments of a voice murmuring soothingly against his skull.

“-get your tail moving, back and forth...that’s right, breathe a little slower there, bubbles, you’re frothing up the water…”

The words are a stream of senseless noise but the familiar, chiding tone breaks through his panic, giving him a soothing tempo to slow his racing soulbeat to. Jerkily, he manages to lift his arms enough to cling back to his savior, his clumsy grip tightening to a painful fervency.

If the prick of Cross’s claws digging into his back bothers Killer, he doesn’t show it. His own touch remains firm but careful as he cradles Cross to his chest. There’s a second set of hands on Cross’s back, gripping under his dorsal fin and around his humerus. Dust’s eyelights are bright and blown with an emotion Cross can’t decipher, something fearsome and dangerous, but his violent intent is being firmly restrained. He matches each stroke of Killer’s tail with a mirrored one of his own, the two of them supporting Cross’s limp, inert weight between them as they climb laboriously back to the top of the crevice.

Even with both of them, it’s a struggle. Cross is longer and larger, his bones dense and tail taut and heavy with muscle. The long scythe of his tailfin drags like an anchor against their upward momentum, but before either can show signs of flagging, Cross feels another body crowd against his back.

“Let me take him,” Horror murmurs, and Dust gratefully shifts to let the larger mer take his place. It takes some coaxing to convince Cross to let Killer go, but with Horror’s murmured reassurance and Killer’s forehead knocking with soft affection against his own, Cross finally reassigns his death-grip. He clings to the safety of Horror’s broad, notched ribcage, face buried resolutely against his shivermate’s sternum. 

“Have you, angelfish,” Horror rumbles. “Going up...gonna get you home.”

Cross’s thoughts are still churning like maelstrom of fighting currents, but dimly he’s struck by the sucker-punch realisation that he’s ruined the hunt. The shiver, Nightmare, Dream, they’ll all go hungry tonight because of him. Because he’s _weak_. A failure. 

( _These results are inadequate, Project X. I expected more from you_.)

“S-sorry,” he manages to gasp, fighting back a twist of self-loathing. “I can go...myself…”

“Nope,” Killer says immediately. “Not happening, Crossy. Boss doesn’t want anyone going out alone anymore. ‘Sides, we don’t leave anyone behind.”

Cross makes a pitiful sound of distress, but the words are an immense relief. He isn’t certain he could handle being on his own right now, or navigate the unfamiliar trails back to Nightmare’s cavern.

It’s only once they crest the top of the canyon that Cross finally manages to draw a proper breath. His blurry vision is slowly starting to clear, but his body still feels as soft and useless as a sea cucumber, the weak twitching of his tail barely offering any assistance to their pace. He’s pathetically grateful they don’t seem to expect him to swim on his own. After a brief deliberation, he’s guided to cling to Horror’s shoulders from behind instead of his chest, allowing the other mer to swim freely and with greater speed as they begin heading for home. 

They head back in the same arrowhead formation, Cross safely ensconced in their midst with Dust and Killer staying close on either side, guarding their vulnerable shivermates. Cross can’t bring himself to lift his face, too ashamed to look at anyone as he tries to muffle his shaky breathing against Horror’s scapula. A deep rumble sounds in Horror’s chest. It’s a sound Cross has never heard any mer make, almost like a low constant growl, except the intonation is placating rather than aggressive. The soothing hum resonates in Horror’s ribcage with a gentle vibration Cross can feel through his own body, steadying him. Belatedly, he realises Killer and Dust are doing it too. The water thrums with the same frequency, strange and intimate and calming.

The arduous journey back to the Grotto seems to pass between one blink and the next. Cross only emerges groggily from his trance when the noise finally tapers off only to be replaced by the louder, deeper boom of Nightmare’s voice.

“What happened?”

Cross looks up and is immediately enveloped by the eerily alluring light of Nightmare’s single eye, bathing them all in its possessive glare. The water roils as Nightmare’s limbs slither out to form a protective cage around the shiver, as if to protect them from any threats that may have followed them home. None of them even get a word out before Cross feels himself being gently pried from Horror’s back, more tentacles gathering him up for the kraken’s inspection.

“I’m fine,” he protests weakly. He ineffectively tries to bat them away, his limbs heavy with unexpected exhaustion. Nightmare’s eye narrows to an unconvinced slit, and Cross finds his struggles effectively halted as Nightmare simply flips him over, leaving him helplessly stunned. “W-wait-!

His plaintive objections go thoroughly ignored but it’s difficult to feel annoyed. Belly up, his body instinctively goes limp and calm, the residual ache in his chest finally receding and the burn in his gills starting to ease. The delicate, suckered tips of Nightmare’s tendrils begin patting him down, checking for any sign of harm. “Hhhhnn...Ni...ght...”

“Shhh,” Nightmare hushes him, bringing him close and wrapping him beneath another coiling tentacle. Instead of feeling crushed or trapped as he did in the abyss, Nightmare’s hold feels like safety, expertly supporting the strengthless curve of Cross’s spine from skull to tail-tip and keeping him safe and shielded from the world.

He’s dimly aware of conversation happening outside his cocoon, but it seems vague and unimportant compared to the way Nightmare is holding him, carefully but firmly. Jelly-soft suckers kiss over his bones and down the length of his tail, easing the raw, abraded feeling of sensory overload left in the wake of his panic. It feels like being wrapped in a layer of sponge, cushioned and protected from the cruelties of the deep. His sockets flutter, struggling to stay open as the familiar grip of Nightmare’s embrace lulls him into a near-doze. It’s hard not to associate Nightmare’s handling with the groggy contentment of a post-feed grooming session, and even without the burden of a full belly making him sluggish he finds himself settling into the same tranquil state. 

Even when Nightmare finally loosens his grip, allowing Cross to reorient himself from his belly-up position, his skull still feels fuzzy with lethargy. He’s disinclined to move, unwilling to leave the comforting tangle of Nightmare’s limbs, but as with his post-feeding fuge his hazy instincts demand he curl up someplace warm and safe until it passes. He makes a soft, plaintive chirp and is rewarded by the swirl of Nightmare’s tentacles curling into the tunnel-shaped nest Cross prefers. He crawls into it gratefully, burying himself in the softness of Nightmare’s body as the tips of tentacles drift over to shade him, swaying like the vines of a kelp forest.

It’s too tempting to forget his usual adherence to his self-imposed regiment and slip into a doze, but as always the unsanctioned nap proves to be a mistake. His dreams feel like another cage, tight and dark and full of stale, dank water and the ragged echo of his own voice crying out in an empty void. He snaps awake on the brink of another wild panic only to be halted by the bright, warm glow suffusing the inside of his hiding spot. The golden hue immediately tells him that he’s not in the abyss, and he’s not in the lab. It, along with the small hand petting the crest of his skull, can mean only one thing, and Cross slumps back against the bed of Nightmare’s tentacles and lets out a tight, heavy breath. “Dream…”

“Cross,” Dream greets, completely unafraid despite how close Cross came to losing control of himself again. He’s perched at the opening to the nest, close enough to comfort without crowding into the small space. His hand strokes along the lines of Cross’s cranial sutures, the contact soothing in its repetition. There’s a small, unfamiliar crease of distress between his sockets. “We were worried about you.”

His concern makes Cross’s insides twist at the thought of the explanation. His pledge to guard the pretty goldfish mer seems reckless and shameful in face of his cowardice. Reminds him that he doesn’t _belong_ here, despite how desperately he wants to think he could.

“Sorry,” he mumbles, then huffs in surprise as one of Nightmare’s tentacles wraps around his waist and gives a reproving squeeze.

“You don’t need to be sorry,” Nightmare tells him, his voice a displaced echo from outside the nest. “I told the idiots not to push you so fast.”

“They got too excited to show you their favourite hunting ground,” Dream agrees with a fond shake of his head. “I hope you can forgive them.”

“Of course,” Cross stammers, taken aback. It isn’t like the others have done anything wrong. _Cross_ is the one who failed, who couldn’t handle a simple task that the rest of the shiver performs daily. And they’d still taken care of him even after he’d proved himself inadequate, though no doubt there'll be some kind of reprimand to follow. Dust’s tongue is scathing, and Killer can never pass up an opportunity to taunt or mock. If Cross endures it gracefully enough, maybe they won’t tell him they no longer want him in the shiver-

“Here!” Dream’s sweet voice interrupts his anxious imaginings, startling Cross out of his thoughts to find a long, silver-scaled Bass being deposited in his lap. There’s a looseness to its head that shows its spine has already been neatly snapped, leaving it dead without so much as a drop of spilled blood. “You should eat something. It’ll help you feel better.”

The generosity of the offering fills Cross with remorse. “No, I...I messed up, you shouldn’t...Dream, don’t go hungry on my account.”

“I’m not!” Dream insists cheerfully. “I already ate. I can hunt for myself you know...don’t give me that look, my brother and I fended for ourselves for a long time before you all came along. And Night could stand to skip a meal or two. His tentacles are starting to look a little plump these days.”

“Excuse me?” Nightmare growls, offended, while Cross tries to smother his sudden, unexpected snort of amusement. Dream looks utterly unrepentant, even pleased with himself as he grins at Cross.

“He hates it because it makes his other form even cuter,” he says in a conspiratorial false-whisper that Nightmare can clearly overhear. “So bottom-heavy and soft-Ah!”

Dream ducks away as an angry tentacle darts out to try and capture him. With a high trill of laughter he flees from its pursuit, using Nightmare’s greater mass against him to hide between his coils.

“I’ll show you who’s bottom-heavy,” Nightmare hisses, though the threat sounds unaccountably affectionate. “Cross, stop staring at that fish and eat it while I teach my brother a lesson.”

An order is easier to accept than an offering, and with only a faint twist of guilt Cross lifts the Bass to his mouth and bites down, taking off a meaty chunk of its tail. He knows he still owes them an explanation -- to Nightmare, Dream and the rest of the shiver -- and he promises himself he will tell them...but for now it’s easier to let himself be plied with food and the show of unexpected playfulness from the two guardians and let the old hurts and fears sink to the back of his mind where he prefers to keep them. 

**Author's Note:**

> You can pry the 'Skeletons can purr' headcanon from my cold dead hands. Yes, even skelesharks can purr, damnit. It's not only for soothing distraught shivermates, but they're also desperately trying to heal whatever hurt Cross has that they can't see.
> 
> It's the first time anyone has purred for Cross. Poor bb still has a lot to learn about his kind.


End file.
